We can block light by placing obstackes in its oath, but its much more diffcult to block sound. why?

Because of the sound waves that can travel through walls. Our ears are very intelligent and can process many sounds. Light rays are different though, because objects can block them because the light rays are not as strong as the sound waves.

(4,-2)

explanation:

6x+4y=16

-6x-9y=-6

-5y=10

y=-2

x=4